Senior Sergeant Fane Troy said after one child died at the scene, the second passed away in Starship Hospital as a result of their injuries. Both children were correctly restrained in car seats, police say.

Another person remains in critical condition in Waikato Hospital.

In a statement, police urged motorists to watch their following distances as they made their way home as the Easter break comes to a close.

Police won't release the age and gender of the deceased until family have been contacted - many are overseas, so they say it could take some time.

Both the serious crash unit and the commercial vehicle safety team are investigating.